Received March 19, 2009; Revision received April 9, 2009
DNA topoisomerases are enzymes responsible for regulation of genomic DNA
supercoiling. They participate in essential processes of cells such as
replication, transcription, recombination, repair, etc., and they are
necessary for normal functioning of the cells. Topoisomerases alter the
topological state of DNA by either passing one strand of the helix
through the other strand (type I) or by passing a region of duplex DNA
through another region of duplex DNA (type II). Type I DNA
topoisomerases are subdivided into enzymes that bind to the 5′-
(type IA) or 3′-phosphate group (type IB) during relaxation of
the cleavable DNA. This review summarizes the literature on type IA DNA
topoisomerases. Special attention is given to particular properties of
their structure and mechanisms of functioning of these enzymes.
KEY WORDS: type IA DNA topoisomerases, structure, reaction
mechanism